Can't speak for those models but I much prefer Vandersteen's entry-level 1Cis to the Magnepan 1.7i. To my ears, the Vandys have better detail, tone, bass depth, note decay and a wider sweet spot. They also require less volume and power to wake up.
The 1.7s had a slightly deeper soundstage and faster mid-bass.
On a more minor note, I find it much easier to get in contact with Vandersteen than Magnepan if questions arise.
